Electrical heating element of the strip type



Jan. 18, 1927.

E. L. WIEGIAND' ELECTRICAL HEATING ELEMENT OF THE STRIP TYPE OriginalFile d August 31v 1923 mut Jan. 18,1927.

UNITED STATES PATENT OFFICE.

EDWIN L. WIEGANILOF DOBMONT BOROUGH, PENNSYLVANIA.

nnnc'rarcnn'nna'rme ELEMENT or, run s'rnrr urn.

Original application fled August 81,

This is a division of my former application, Serial No. 660,294, filedAugust 31, 1923, and the subject matter of the present case isrestricted to a so-called strip heater 6 which is one of the severalforms of the invention disclosed in said application.

My earlier application relates generally to a noveltype of electricalheating device or element consistinggenerally of a resistor l envelopedin a body or compressed mass of refractory material encased in a sheetmetal cover or sheath, the primary object of the invention being toprovide an electrical heating device or element affording the maximumoutput of heat at a given temperature, while providing ample safeguardagainst a possible breaking down of the insulation between the resistorand the sheath or cover. Such a construction permits very intimate 2contact between the heat radiating surface of the heating device orelement and the object to be heated and afiords unusual diffusion orspreading out of the enveloped resistor and nearness of the resistor-the2 source of heat--to said object. Numerous other advantages arising fromsuch a construction are set forth in my former application and it isdeemed unnecessary to repeat them here, and in the earlier case theirim- 3 portance is emphasized by a comparison of my improved evice orelement with rior forms of electrical heating devices 0 the same generalclass. 1 As above stated, the present case has to do particularly withstrip heaters which have acquired a distinct place in the art.

Such heaters are employed for various purposes. They may be applied to-alate for heating it; or they may be suspen ed from suitable supports forheating space; or they may be applied to the exterior or interior of avessel for heating the contents thereof; or they may be disposed insidea hollow heating or drying roll. In the past, the more common forms ofthis general type of heater employed the usual resistor wire disposedbetween sheets of mica, the mica, in turn, being enclosed by and betweenstrips of sheet metal which, form a sort of easing that .is open at itsends. 7

An advantage which my improved strip heater possesses over these earlierforms is thatit maybe readily bent .to conform to object'spfjid-ifi'erent shapes to which it may 1928, Serial No. 66 0394. Dividedand this application filed larch 7, 1824. Serial No. 697,446.

and resistor which results in a breaking up and displacement of the micasheets or lay-' ers and the resistor and an egrees of some of thedisintegrated mica through the open ends of the casing. Furthermore, thecasing, being open at.its ends, permitted ingress of moisture and otherdamagin elements.

Among the several objects 0 my present invention are to provide anelongated, narrow and comparatively thin electrical heating devicecomprising a resistor element enveloped within a body of refractory,electrical insulating,'heat conducting material that is encased within asheet metal cover or sheath; to provide, in such a construction, acasing that is completely closed against the ingress of deterioratingagents, as moisture and foreign substances; to provide, in aconstruction of the foregoing nature, a casing composed of two sheetmetal members, one preferably in the form of a channel, and the other acover between which coverand the web of the channel, the resistor,enveloped in the body of refractory material, is disposed, the edges ofthe channel being turned over the cover and com pressed to hold theparts firmly together; and also to close the ends of the casing bypressing the extremities of the cover and end extensions of the web ofthe channel the scope of its intended use, and is so designed andconstructed as to expedite manufacture, and insure production at a lowcost.

The foregoing objects, with others hereinafter appearing, are attainedin the embodiment of the invention illustrated in the accompanyingdrawing wherein Fig. l is at plan view and Fig. 2 is a side elevation ofmy improved strip heater; Fig. 3 is a longitudinal section through oneend of the heater on a somewhat enlarged scale; Figs. 4 and 5are'transverse sections Qn'the same scale as Fig. 3, the heater beingshown as flat in the former view and as being transversely curved in thelatter view; Figs. 6 and 7 show the strip heater bent to differentforms; and Fig. 8 is a fragmentary plan view of a perforated cover thatis employed in some instances.

Describing the construction by the use of reference numerals, 1 denotesthe resistor which preferably, but not necessarily consists of asuitable metallic ribbon or flat wire that is preferably bent intoserpentine form. This resistor is completely enveloped by a compacthomogeneous mass of granular refractory electrical insulating material 2which not only supports the ribbon at all points due to its intimatecontact therewith but also prevents oxidation of the resistor. Each endof the resistor is connected to a terminal 3 which may be of anysuitable type but is preferably similar to that disclosed in myco-pending application Serial No. 555,870, filed April 21, 1922. Theseterminals are each provided with insulating washers 4 which preventcontact of the terminals with the sheet metal casing composed of achannel receptacle 5 and a cover plate6 which completely surround therefractory material. The side edges 7 of the receptacle are deflectedover the cover plate, as clearly shown in'Figs. 1, 4 and 5, and the endsof the casing beyond the terminals 3 are flattened, as indicated at 8,and are provided with apertures 9 so that the heater may be convenientlysupported on a frame or fastened to an object to be heated, If desiredthe seams formed by the overlapping side edges 7 and the cover plate 6may be welded, although for ordinary, conditions folding over the edgesunder high pressure will prove sufiicient.

In some instan ces where it is unnecessary to provide a tight seal forthe insulating material, I perforate a portion of the metal casing asfor example the cover plate 11, as

shown in Fig. 8. During the folding and pressing of the side edges ofthe casing, the

refractory material will be forced into the perforations and therebyserve to bond the refractory material and easing together.

A strip heating element of this general character is very thin, light inwei ht, and affords maximum transfer of heat from the resistor to theobiect to be heated. The resistor is complete y enveloped in a compactmass of: refractory material and hence is supported at all points and iscompletely protected against oxidation. These strip heaters may belongitudinally or laterally bent to various shapes to meet theparticular requirements.

In Fig. 5 I have shown the strip heater bent to assume anarcuate,cross-section while in Figs. 6 and 7' I'have shown the elementbent into circular form and U-shape form, respectively. The circularform may be conveniently applied to any cylindrical object as forexample a pipe or Water tank, while the U-shape form is suitable for aplication to molds and similar objects. bent into circular form, as inFig. 6, a bolt 12 may be engaged through apertures 9 for the purpose ofretaining the element in position on the object.

While, so far as the present invention is concerned, I do not limitmyself to any particular kind of refractory insulating material, onekind found especially suitable for the purpose is composed of magnesiumor aluminum oxide or zirconium silicate, either individually wherepossible or a compound of them, together when desirable with a bindingmaterial such as clay, to give the necessary plasticity duringfabrication and to effect homogeneity in the final product." Neither doI limit myself in the broad analysis of the invention to a sheath orcover constructed in the manner illustrated, as obviously the same mighttake various forms amlQr-onstructions without departing from the spiritof the invention.

The resistor element may be enveloped in therefra'ctory insulatinmaterial in accordance with my Patent o. 1,136,076, issued April 20,1915, entitled Process of producing electrical heating devices, or inaccordance with my latent No. 1,398,410 issued November 20, 1921, andentitled Fmbeddin process.

IF aving thus described my invention, what I claim 1s:

1. As a new article of manufacture, an electrical heating element of thestrip type, as distinguished from electrical stoves, hot plates andtubular heaters, the same comprising a resistor, an elongated, narrow,relatively thin sheet metal sheath made up of a plurality of partsenveloping said resistor and spaced therefrom, and'a mass of granularrefractory electrical insulating material of high heat conductingquality filling the space between. the resistor and sheath, the resistorbeing provided with terminals each accessible through an opening in thesheath. v

2. As a new article of manufacture, an electrical heating element of thestrip type comprising a resistor, an elongated, narrow hen electricalheating element of the strip type comprising a resistor arranged in flatforsheet metal sheath made up sheet metal sheath made up of a pluralityof parts enveloping said resistor and spaced therefrom, and anartificially compacted mass of granular refractory electrical insulatingmaterial filling the space between the resistor and sheath, the resistorbeing provided with terminals each accessible through an opening in thesheath.

3. As a new article of manufacture, any

electrical heating, element of the strip type comprising a resistor, anelongated, narrow of a plurality of parts enveloping said resistor andspaced therefrom, and a mass of granular refractoryelectricalinsulating' material filling the space between the resistorand the sheath,

the ,entire as:en1bly being in a highly compacted state, the resistorbeing provided with terminals each accessible through an opening in thesheath. I

.4. As a new article of manufacture, an

mation, an'elongated,-narrow sheet metal sheath made up of a pluralityof parts enveloping said. resistor and spaced therefrom, and anartificially compacted massof granular refractory electrical insulatingmaterial filling the space between the resis-' tor and sheath, theresistor bein provided with terminals each accessible t rough an openingin the sheath.

- 5. As a new article of manufacture, an

as distin electricagltileating element of the strip type,

ished from electrical stoves, hot

' plates and tubular heatersgthe same comprising a resistor, anelongated, narrow, relatively thin, seamed sheet metal sheath envelopingsaid resistor and spaced therefrom,

and a mass of granular refractory electrical insulating material of highheat conducting quality filling the space between the resistor andsheath, the resistor being provided with terminals each accessiblethrough an opening in the sheath. 7

6. As a new article of manufacture, an electrical heating element of thestrip type comprising a resistor,-' 'an elongated, narrow seamed sheetmetal sheathenveloping said resistor and spaced therefrom, and anartificially compacted mass of granular refractory electrical insulatingmaterial, filling the space between the resistor and sheath, theresistor being provided, with terminalseach accessible through anopeningin the sheath.

7. As a new article of manufacture, an electrical heating element of thestrip type,

as distinguished from electrical stoves, hot

platgs and tubular heaters, the same comprising a resistor arranged inflatformation, an elongated, narrow, relatively-thin sheet metal sheathenveloping said resistor and spaced therefrom and being oblong incroSssection, and a inass of granular rev fractory electrical insulatingmaterial of high heat conducting quality filling the space between theresistor and the s eath,

sulating material of hi h heat conducting quality filling the spacetween the resistor and the sheath, the sheath consisting of two mainparts closely embracing and envfeloping said mass of insulatingmaterial, and the resistor bein provided with terminals each accessiblet roughan opening in the sheath. 7

9. 'As a new article-of manufacture, an electrical heating element ofthe strip type comprising a resistor, an elongated, narrow sheet metalsheath enveloping said resistor and spaced therefrom, and a mass ofgranular refractory electrical insulating material fillin the spacebetween the resistor and the provided with'terminals sheat the sheath'being cldsed at its ends by the pressed together opposed walls of thecasing, and the resistor bein provided with terminals each accessiblethrough an opening in the sheath.

10.;Asa new article of manufacture, an

electrical heating element of the strip type comprising a resistor, anelongated, narrow sheet metalsheath enveloping said resistor and spacedtherefrom, and a mass of granular refractory electrical insulatingmaterial filling the space between the resistor and the sheath, theresistor being provided with) terminals each accessible through anopening in the sheath, the element having a relatively thin crosssection to ermit bending of said elementto various s apes.

11. As a new article of manufacture, an

electrical heating element of the striptype,

as distinguished .from electrical stoves, hot

plates and tubular heaters, the same comprising aresistor, an elongated,narrow, relatively thin sheet metal sheath enveloping said resistor andspaced therefrom, and a mass of. granular refractory electricalinsula'ting material of high heat conducting quality filling the spacebetween the resistor and the sheath, the resistor being provided withterminals each accessible through an opening in the sheath, the elementhaving a relatively thin cross section and formed to a desired shape. rY

12. As .a new article of manufacture, an electrical heating element ofthe strip type comprising a resistor, an elongated, narrow seamed sheetmetalsheath enveloping said, resistor and spaced therefrom, and anart-ificially compacted mass of granular refracresistor and spacedtherefrom, and an artifitory electrical insulating material filling thecially com acted mass of granular refracspace between the resistor andsheath, the tory electrical insulating material filling the resistorhaving terminals each accessible space betweeh the resistor and sheath,,the 5 through an opening in the wall of the resistor having terminalseach accessible sheath intermediate itsends. through an opening in thewall of the 13. As a new article of manufacture, an sheath. electricalheating element of thestrip type In testimony whereof, I hereunto aflixmy comprising a resistor, an elongated, narrow; signature.

formed sheet metal sheath enveloping 'sai EDWIN L. WIEGAND.

